NHS trusts and primary care organisations must make money available to fund treatments recommended by NICE.

Doctors are expected to follow NICE guidance or to be able to give very good reasons for not doing so.

How does it decide which treatments should be available?

NICE embarks on a long consultation process before deciding whether treatments should or should not be available to patients on the NHS.

It consults the pharmaceutical industry, the medical profession and patients.

In August 2002, NICE established a citizens council representing the general public to give its views on its work.

NICE makes recommendations on which drugs and treatments should be available to the government.

It assesses whether the treatments benefit patients, whether will the NHS to meet key targets like reducing deaths from heart disease and cancer, and whether they are cost-effective.

The health secretary and the health minister in Wales decide whether its decisions should be implemented.

Why is it controversial?

By the very nature of its work, NICE was always going to court controversy.

It is after all deciding whether patients should get the drugs and treatment many of them believe they need.

It is also trying to balance the interests of sometimes very disparate groups - patients, doctors and the pharmaceutical industry.

In July 2002, the influential Commons health committee called for NICE's decision making process to be made more transparent and fairer.

However, MPs also suggested NICE had been criticised unfairly in some instances and called on the government to be more open about rationing or restricting treatment in the NHS.

But they did criticise NICE for failing to make rulings on new drugs quickly enough, leaving many patients and doctors in limbo when hyped drugs come on the market.

What decisions have been controversial?

Among its most controversial decisions, was the ruling in June 2000 not to recommend that beta interferon should be available to every patient with multiple sclerosis.

In August 2002, NICE came under fire again, this time over the drug Glivec. It has previously ruled that the drug should only be given to a handful of patients with leukaemia only to change its mind after stinging criticism from patients and doctors.

More recently, NICE has been criticised for acting too slowly to make decisions over drugs for Alzheimer's disease and bowel cancer.